1. Field of the Invention
This invention relates to an exhaust bypass valve assembly for closing and opening an exhaust bypass for controlling rotations of an exhaust gas turbo-supercharger mainly installed in a spark ignition internal combustion engine whose intake flow is controlled by a throttle valve.
2. Description of the Prior Art
It has been known to control the rotations of an exhaust gas turbo-supercharger by means of an exhaust bypass valve provided in a bypass through which part of exhaust gases passes without passing through a turbine in order to prevent a pressure upstream of a throttle valve from being extraordinarily raised by a compressor driven by the turbine.
For the purpose of controlling the exhaust bypass valve, it has been proposed to move the valve by a deforming movement of a diaphragm caused by a pressure introduced from the upstream of the throttle valve into a chamber of a diaphragm device.
Such a diaphragm device of the prior art controls the upper limit of the pressure upstream of the throttle valve, for example, at 400 mmHg. However, most of gasoline engines for automobiles are operated under partially loaded conditions during normal travelling where throttle valves are partially opened and thus exhaust gas turbo-supercharger rotate at lower speeds. When the pressure upstream of the throttle valve becomes lower than, for example, 400 mmHg in this manner, the exhaust bypass valve closes to cause all the exhaust gases to flow through the turbine, so that the turbine is forced to rotate even when the supercharging is not needed and the exhaust gas resistance would increase to lower the output and thus increase the fuel consumption.